COMTES – Cleaner coal, extra energy

Coal technology has advanced over the years and twice as much electricity is generated from one kilogram of hard coal today than in the 1950s. Soot and gas from coal-fired power stations has been slashed, reducing the impact on climate change. But coal is still seen as a dirty power source, and inefficient to boot. Now, however, a European Union (EU) research project is looking at ways to build a new next generation of fossil based power stations,like coal-fired and gas-fired, by developing nickel-based materials and components that withstand higher temperatures. This could cut greenhouse gas emissions by up to a third and at the same time generate a third more electricity than conventional power plants.

The COMponent TESt Facility for a 700°C power plant project, or COMTES700, aims to improve the overall efficiency of coal fired power plants from the current EU average of 36% to over 50%.

Coal still accounts for 41% of the world's gross power generation, and 26.5% in the EU. Although the EU is working to cut its greenhouse gas emissions from fossil fuels, it will have to continue burning coal for some decades to come as energy demand rises. At the same time, many existing power stations are nearing the end of their lives and will soon need replacing. "The challenge is thus to find ways of making these plants as clean and efficient as possible," says Franz Bauer, COMTES700's original project coordinator.

In today's best-performing plants, the steam produced by the burning coal is piped into the turbines that drive the generators at a temperature of 605° and a pressure of 280 bars. "COMTES700 aims to raise these conditions to 700° and 350 bars by developing highly-resistant, advanced components made from nickel-based materials," says Bauer, who also works for the European power generation association VGB PowerTech.

The COMTES700 research consortium is composed of a group of 17 major European power producers and other players in the field of power generation. It initially ran from 2004 to 2011, and was backed by a €6.1 million grant from the European Commission. A follow-up project, COMTES+, is running from 2011 to 2017, with a €10 million Commission grant.

The project is testing every aspect of how new, advanced components perform in next generation coal-fired power stations. It also opens up the prospect of using Carbon Capture and Storage (CCS) technologies - bringing carbon emissions down to near zero - thereby reducing greenhouse gases still further.

At facilities like E.ON's plants in Gelsenkirchen, Germany, researchers have been testing major boiler components, such as evaporators, superheater tubes, high pressure headers, and high pressure piping, as well as large high pressure bypass, safety and turbine valves. "Nickel-based alloys are being used as they withstand the heat and pressure of the new system better than the steel used in conventional power stations. They are also completely novel in power station construction," says Bauer.

The test facilities are scheduled to operate for 20,000 hours, giving the project team ample time to identify major problems, determine the specifications for the components and work out the optimum operating conditions.

Bauer says that the research is not just of use for the coal and gas sectors, but could be adapted to concentrated solar power plants, and the nickel-based components could even be spun off for aerospace applications. But for coal and gas, he expects it to be in use by the early 2020s.